Powder spray systems are well known. Representative systems are disclosed, for example, in U.S. Pat. Nos. 4,910,047, 4,723,505 and 5,261,934, and in International Pat. App. No. PCT/GB94/00253 (published as WO95/10365), all of which are assigned to Nordson corp. of Westlake, Ohio 44145, who is the assignee of the present invention.
As disclosed in the aforementioned patents, the practice of powder coating involves spraying (with a spray gun) a dry powdered coating material onto a substrate (workpiece), and thereafter heating the substrate and the powder so that the powder melts. Upon cooling, the melted powder forms a solid, continuous coating on the substrate. Often, an electrostatic charge is applied to the sprayed powder, and the substrate is electrically grounded, to increase to increase adhesion of the powder to the surface of the substrate.
Prior art powder spraying (deposition) is typically performed in a containment system such as in a spray booth or under a canopy so that any oversprayed powder ("overspray") can be collected (reclaimed), processed if necessary, and re-used.
Overspray is powder coating material which either misses the substrate being coated (i.e., it is not deposited onto the surface of the substrate), or which rebounds from, or which is deflected by the substrate, and ends up on other surfaces, particularly grounded surfaces, of the spray booth, such as walls of the spray booth and components of the conveyor system which supports the substrate being coated in the spray booth. Typically, parts (substrates) being coated are suspended from the conveyor or carried on the conveyor through the spray booth.
The containment and collection (reclaiming) of overspray particles is important since the powder material is often very expensive. Reclaiming oversprayed powder in a spray booth is typically implemented by an exhaust system which creates a negative pressure within the spray booth and draws the powder entrained in a stream of air out of the spray booth into a powder recovery unit or module (powder collector). In the powder collector, particles of powder are separated from the air in which they are entrained by a one or more filters, collected in a hopper, after which the powder particles may be disposed of or sieved and re-supplied to the spray gun.
The prior art discloses the use of cyclone separators either instead of, or in conjunction with, filter cartridges. Such cyclone separators are effective in removing a majority of the oversprayed powder from the spray booth exhaust air and are generally easier to clean than filters because very little powder is deposited inside the cyclone housing. Cyclone separator are typically of either the tangential-feed of vertical-feed types. Both types operate on the principle of imparting a circumferential velocity to air-entrained overspray powder particles so that the powder particles are separated from the air by the combined effects of centrifugal and gravitational forces and fall to the bottom of the separator, there to be collected and removed (or treated and recycled or reclaimed). The remaining air, substantially stripped of overspray powder particles, is exhausted to the atmosphere or passed through a module containing a number of filter cartridges to remove any residual fine powder particles remaining entrained in the exhaust air.
Relevant concerns in powder spray systems include ensuring complete and efficient removal of overspray from the spray booth and components thereof, as well as ease of maintenance. For example, in large-scale manufacturing operations, it is not enough to simply contain and collect overspray. Due to the cost of the powder materials involved, it is also highly desirable to reclaim the overspray for re-use in the powder coating system.
The present invention advantageously employs several components of prior art powder spray systems, as described hereinabove, which are well known in the art and which require little, if any, further elaboration other than how they are integrated into the powder spray system of the present invention.